Modern research on power supply is not only directed at the enhancement of power density of the power supply, but also devoted to the reduction of working loss of the power supply, as disclosed in Taiwan patent no. 1400603, the patent disclosing a power allocating apparatus used for a plurality of power supply modules, each power supply module being coupled to a plurality of loads via a plurality of power lines, respectively. The power allocating apparatus includes a first switch element, a second switch element and a control device. The first switch element is provided with a first connecting terminal and a second connecting terminal coupled to an output terminal of a power supply module with a relatively high conversion efficiency and an output terminal of a power supply module with a relatively low conversion efficiency, respectively, in the plurality of power supply modules, and allowed to selectively allocate a power generated by the power supply module with the relatively high conversion efficiency to a predetermined number of loads simultaneously according to on or off states. The second switch element is coupled between the output terminal of the power supply module with the relatively low conversion efficiency and the second connecting terminal of the first switch element, in which the second switch element is not conductive when the first switch element is conductive. Moreover, the control device is coupled to the first switch element for generating the control signal to control the first switch element to enter an on state or an off state.
It is known from the brief description and figures of that patent, the diode is used as the switch element in that patent. Nevertheless, the diode is turned on only when obvious voltage difference between positive and negative terminals of the diode appears (due to forward-bias of 0.7V of the diode). However, the voltage outputted from the power supply module with the relatively high conversion efficiency used in place of the power supply module with the relatively low conversion efficiency is the same as that outputted from the power supply module with the low conversion efficiency; that is to say, 5V of the power supply module with the relatively high conversion efficiency is used in place of 5VSB outputted from the power supply module with the relatively low conversion efficiency. Therefore, the output of the power supply module with the relatively high conversion efficiency being used in place of that of the power supply module with the relatively low conversion efficiency is not ensured by the technology proposed in that patent.